Providing an absorption pad which shows remarkable water absorptivity and can shorten a detection time when employed for an immunoassay apparatus. A water absorption pad for the immunoassay apparatus, containing 50% by weight or more of silicon-containing particles wherein a moisture absorptivity is 30% or less at a humidity of 60% or less and a moisture absorptivity is 40% or more at a humidity of 90% or more, a strip for an immunoassay using said absorption pad as a suction part, and an immunoassay apparatus including said strip for the immunoassay.